Our invention relates to a method of discriminating between flexible magnetic disk cartridges or assemblies of two different storage capacities (e.g. one-megabyte and 4-megabyte (MB)) preparatory to formatting as either of the two types of unformatted disk assemblies is loaded in an associated data transfer apparatus. Our invention also concerns the data transfer apparatus having provisions for such discrimination.
Flexible magnetic disk cartridges have for years been commercially available in capacities of 1 MB and 2 or 1.6 MB, the latter being known as the high density type. The disk cartridge of the 2-MB capacity has a notch in its housing so that on being loaded in a disk drive, the 2-MB disk cartridge is automatically identified as such. The user has had no trouble in discrimination between the 1- and 2-MB disk cartridges.
More recently, however, a 4-MB disk cartridge has been developed, offering the user a choice among three different storage capacities. A careful user can, of course, make proper use of the three different types of disk cartridges. Not all users can possibly be expected to be so careful.
It is therefore essential that data transfer systems for use with such different types of disk cartridges be equipped to automatically discriminate between them as such cartridges are loaded therein. For example, an unformatted 4-MB disk cartridge may be inadvertently inserted in the disk drive when the data transfer system comprising the disk drive is conditioned for formatting 1-MB disk cartridges. Then the 4-MB disk will be initialized with the format for 1-MB disks.
An obvious measure to prevent the noted inconvenience might be to form a notch or the like in the housing of the 4-MB disk cartridge and to provide the disk drive with means for optically or mechanically detecting the notch as the 4-MB disk cartridge is loaded therein. The disk drive would then be capable of distinguishing the 4-MB disk cartridge from the 1-MB one. We object to this solution because it would make the disk drive unnecessarily complex in construction, adding substantially to its manufacturing cost.